Ascorbic acid has activities such as inhibition of lipid peroxide production, acceleration of collagen production, retardation of melanin formation and enhancement of immune functions or performances. For these purposes, ascorbic acid has heretofore been used in the fields of medical or pharmaceutical preparations, agricultural chemical preparations, animal or veterinary drug preparations, foods, animal feeding stuff, cosmetic preparations, etc. However, ascorbic acid has poor stability with the elapse of time and poor lipid solubility. Accordingly, the amount of ascorbic acid which has permeated through the cell membrane and has cumulated in cells is rather limited, and the physiological actions of vitamin C cannot necessarily be achieved to a satisfactory extent, if the ascorbic acid per se is used. In order to improve the stability of ascorbic acid, various derivatives thereof have been proposed, such as one wherein the hydroxyl group present in the enediol portion at the 2- or 3-position, which is susceptible to oxidation, is converted into a phosphoric acid ester as described in, e.g., JP-B (examined Japanese patent publication) 52-1819 (Patent Document 1), and JP-A (unexamined published Japanese patent application) 02-279690 (Patent Document 2), or one wherein the acylation thereof is effected with a fatty acid so as to improve the lipid solubility, as described in, e.g., JP-A-59-170085 (Patent Document 3). However, there are very few derivatives which have been improved both in stability and in lipid solubility.
As for the ascorbic acid which has been improved both in stability and in lipid solubility, JP-A-61-152613 (Patent Document 4) describes a cosmetic composition containing a 6-O-higher-acyl ascorbic acid-2-phosphoric acid ester salt. However, in this patent publication, a process for producing a sulfuric acid ester (but not a phosphoric acid ester) thereof is described, a process for producing a phosphoric acid ester thereof is not described, and the ascorbic acid derivative, the provision of which is described in this publication, is not identified. From these points, it is difficult to recognize that the 6-O-higher-acyl ascorbic acid-2-phosphoric acid ester is disclosed in this publication so as enable the practice thereof.
JP-A-10-298174 (Patent Document 5) describes a process for producing 6-O-higher-acyl ascorbic acid-2-phosphoric acid ester and results of the structure determination of the substance. It is stated that the 6-O-higher-acyl ascorbic acid-2-phosphoric acid ester produced by this process is improved both in stability and in lipid solubility, and the uptake thereof into cells is facilitated. However, among these substances, ascorbic acid-2-phosphoric acid ester-6-palmitatic acid ester sodium salt and an aqueous solution thereof are not yet satisfactory in view of the stability thereof.
Patent Document 1: JP-B-52-1819
Patent Document 2: JP-A-02-279690
Patent Document 3: JP-A-59-170085
Patent Document 4: JP-A-61-152613
Patent Document 5: JP-A-10-298174